Method and apparatus for measuring pore pressure beyond the casing

Abstract

Acoustic waves from a controllable downhole acoustic source in a cased borehole are focused into a region of an earth formation. A hydrophone is used to monitor acoustic signals for onset of cavitation. The estimated pressure from the source in the focus region provides an estimate of formation pore pressure.

What is claimed is: 
     
       1. A method of estimating a formation pore pressure of an earth formation, the method comprising:
 using an acoustic source inside a borehole for producing an acoustic wave in the formation; 
 using a sensor for producing a signal indicative of a cavitation in the earth formation resulting from the produced acoustic wave; and 
 using a processor for estimating the formation pore pressure from the produced signal. 
 
     
     
       2. The method of  claim 1  wherein producing the acoustic wave further comprises producing a focused acoustic wave. 
     
     
       3. The method of  claim 2  wherein producing the focused acoustic wave further comprises using a device selected from: (i) a curved transducer, and (ii) a plane transducer in conjunction with a focusing device. 
     
     
       4. The method of  claim 1  wherein estimating the formation pore pressure further comprises extrapolating a power of the acoustic source into the earth formation. 
     
     
       5. The method of  claim 1  wherein estimating the formation pore pressure further comprises applying a correction for attenuation, reflection and propagation effects. 
     
     
       6. The method of  claim 1  further comprising using the estimated formation pore pressure for at least one of: (i) controlling a secondary recovery operation, (ii) selecting a zone in the casing for perforation, (iii) indicating of completion, and (iv) identifying sand and shale laminations. 
     
     
       7. The method of  claim 1  further comprising conveying the acoustic source into the borehole on an umbilical. 
     
     
       8. The method of  claim 1  further comprising using, as the sensor, a hydrophone. 
     
     
       9. The method of  claim 1  further comprising using the acoustic source in a cased borehole. 
     
     
       10. An apparatus configured to estimate a formation pore pressure of an earth formation, the apparatus comprising:
 an acoustic source configured to produce an acoustic wave in the earth formation from inside a borehole; 
 a sensor configured to produce a signal of a cavitation in the earth formation resulting from the produced acoustic wave; and 
 a processor configured to estimate the formation pore pressure from the produced signal. 
 
     
     
       11. The apparatus of  claim 10  wherein the acoustic source is further configured to produce a focused acoustic wave. 
     
     
       12. The apparatus of  claim 11  further comprising a device configured to produce the focused acoustic wave, the device being selected from: (i) a curved transducer, and (ii) a plane transducer in conjunction with a focusing device. 
     
     
       13. The apparatus of  claim 10  wherein the processor is configured to estimate the formation pore pressure by extrapolating a power of the acoustic source into the earth formation. 
     
     
       14. The apparatus of  claim 10  wherein the processor is configured to estimate the formation pore pressure by applying a correction for attenuation, reflection and propagation effects. 
     
     
       15. The apparatus of  claim 10  wherein the processor is configured to use the estimated pore pressure for at least one of: (i) controlling a secondary recovery operation, (ii) selecting a zone in the casing for perforation, (iii) indicating a quality of completion, and (v) identifying sand and shale laminations. 
     
     
       16. The apparatus of  claim 10  further comprising an umbilical configured to convey the acoustic source into the borehole. 
     
     
       17. The apparatus of  claim 10  wherein the sensor further comprises a hydrophone. 
     
     
       18. The apparatus of  claim 10  wherein the borehole further comprises a cased borehole. 
     
     
       19. A computer-readable medium product having stored thereon instructions that when read by at least one processor enable the at least one processor to perform a method, the method comprising:
 estimating a formation pore pressure of an earth formation using a signal responsive to a cavitation in the earth formation resulting from use of a focused acoustic source inside a borehole, and a power of the acoustic source. 
 
     
     
       20. The computer-readable medium of  claim 19  further comprising at least one of: (i) a ROM, (ii) an EPROM, (iii) an EEPROM, (iv) a flash memory, and (v) an optical disk.